Women are increasingly at risk of not only becoming HIV infected but also at risk of passing it on to their unborn children. Zidovudine (ZDV) has been found to have significant clinical benefits in adults. This study proposes to introduce ZDV during the third trimester of a woman's pregnancy and evaluate its safety and pharmacokinetics in women and their children. All unborn children of women participating in this study are at risk for HIV-1 infection.